Magnetic tape device and magnetic reproducing method employing TMR head and magnetic tape having characterized magnetic layer

ABSTRACT

The magnetic tape device includes: a magnetic tape; and a reproducing head, in which the reproducing head is a TMR head, the magnetic tape includes a non-magnetic support, and a magnetic layer including ferromagnetic powder, a binding agent, and fatty acid ester on the non-magnetic support, a full width at half maximum of spacing distribution measured by optical interferometry regarding a surface of the magnetic layer before performing a vacuum heating with respect to the magnetic tape is greater than 0 nm and equal to or smaller than 7.0 nm, a full width at half maximum of spacing distribution measured after performing the vacuum heating is greater than 0 nm and equal to or smaller than 7.0 nm, and a difference between a spacing measured by optical interferometry regarding the surface of the magnetic layer after performing the vacuum heating with respect to the magnetic tape and a spacing measured before performing the vacuum heating is greater than 0 nm and equal to or smaller than 9.0 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2016-254444 filed on Dec. 27, 2016. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape device and a magneticreproducing method.

2. Description of the Related Art

Magnetic recording is used as a method of recording information in arecording medium. In the magnetic recording, information is recorded ona magnetic recording medium as a magnetized pattern. Informationrecorded on a magnetic recording medium is reproduced by reading amagnetic signal obtained from the magnetized pattern by a magnetic head.As a magnetic head used for such reproducing, various magnetic headshave been proposed (for example, see JP2004-185676A).

SUMMARY OF THE INVENTION

An increase in recording capacity (high capacity) of a magneticrecording medium is required in accordance with a great increase ininformation content in recent years. As means for realizing highcapacity, a technology of increasing a recording density of a magneticrecording medium is used. However, as the recording density increases, amagnetic signal (specifically, a leakage magnetic field) obtained from amagnetic layer tends to become weak. Accordingly, it is desired that ahigh-sensitivity magnetic head capable of reading a weak signal withexcellent sensitivity is used as a reproducing head. Regarding thesensitivity of the magnetic head, it is said that a magnetoresistive(MR) head using a magnetoresistance effect as an operating principle hasexcellent sensitivity, compared to an inductive head used in the relatedart.

As the MR head, an anisotropic magnetoresistive (AMR) head and a giantmagnetoresistive (GMR) head are known as disclosed in a paragraph 0003of JP2004-185676A. The GMR head is an MR head having excellentsensitivity than that of the AMR head. In addition, a tunnelmagnetoresistive (TMR) head disclosed in a paragraph 0004 and the likeof JP2004-185676A is an MR head having a high possibility of realizinghigher sensitivity.

Meanwhile, a recording and reproducing system of the magnetic recordingis broadly divided into a levitation type and a sliding type. A magneticrecording medium in which information is recorded by the magneticrecording is broadly divided into a magnetic disk and a magnetic tape.Hereinafter, a drive including a magnetic disk as a magnetic recordingmedium is referred to as a “magnetic disk device” and a drive includinga magnetic tape as a magnetic recording medium is referred to as a“magnetic tape device”.

The magnetic disk device is generally called a hard disk drive (HDD) anda levitation type recording and reproducing system is used. In themagnetic disk device, a shape of a surface of a magnetic head sliderfacing a magnetic disk and a head suspension assembly that supports themagnetic head slider are designed so that a predetermined intervalbetween a magnetic disk and a magnetic head can be maintained with airflow at the time of rotation of the magnetic disk. In such a magneticdisk device, information is recorded and reproduced in a state where themagnetic disk and the magnetic head do not come into contact with eachother. The recording and reproducing system described above is thelevitation type. On the other hand, a sliding type recording andreproducing system is used in the magnetic tape device. In the magnetictape device, a surface of a magnetic layer of a magnetic tape and amagnetic head come into contact with each other and slide on each other,at the time of the recording and reproducing information.

JP2004-185676A proposes usage of the TMR head in the magnetic diskdevice. On the other hand, the usage of the TMR head in the magnetictape device is currently still in a stage where the further use thereofis expected. The reason why the usage thereof is not yet practicallyrealized is because it is not necessary that a reproducing head used inthe magnetic tape device have sensitivity improved enough for using theTMR head. Nevertheless, in a case where the TMR head can be used as thereproducing head even in the magnetic tape device, it is possible todeal with higher-density recording of a magnetic tape in the future.

Therefore, an object of one aspect of the invention is to provide amagnetic tape device in which a TMR head is mounted as a reproducinghead.

A magnetoresistance effect which is an operating principle of the MRhead such as the TMR head is a phenomenon in which electric resistancechanges depending on a change in magnetic field. The MR head detects achange in leakage magnetic field generated from a magnetic recordingmedium as a change in resistance value (electric resistance) andreproduces information by converting the change in resistance value intoa change in voltage. It is said that a resistance value of the TMR headis generally high, as disclosed in a paragraph 0007 of JP2004-185676A,but generation of a significant decrease in resistance value in the TMRhead may cause a decrease in reproduction output and a deterioration ofelectromagnetic conversion characteristics (specifically,signal-to-noise-ratio (SNR)) accompanied with that.

During intensive studies for achieving the object described above, theinventors have found a phenomenon which was not known in the relatedart, in that, in a case of using the TMR head as a reproducing head inthe magnetic tape device, a significant decrease in resistance value(electric resistance) occurs in the TMR head. A decrease in resistancevalue of the TMR head is a decrease in electric resistance measured bybringing an electric resistance measuring device into contact with awiring connecting two electrodes configuring a tunnel magnetoresistanceeffect type element included in the TMR head. The phenomenon in whichthis resistance value significantly decreases is not observed in a caseof using the TMR head in the magnetic disk device, nor in a case ofusing other MR heads such as the GMR head in the magnetic disk device orthe magnetic tape device. That is, occurrence of a significant decreasein resistance value in the TMR head in a case of reproducing informationby using the TMR head as a reproducing head was not even confirmed inthe related art. A difference in the recording and reproducing systembetween the magnetic disk device and the magnetic tape device,specifically, contact and non-contact between a magnetic recordingmedium and a magnetic head at the time of the reproducing may be thereason why a significant decrease in resistance value of the TMR headoccurred in the magnetic tape device is not observed in the magneticdisk device. In addition, the TMR head has a special structure in whichtwo electrodes are provided with an insulating layer (tunnel barrierlayer) interposed therebetween in a direction in which a magnetic tapeis transported, which is not applied to other MR heads which arecurrently practically used, and it is considered that this is the reasonwhy a significant decrease in resistance value occurring in the TMR headis not observed in other MR heads.

With respect to this, as a result of more intensive studies afterfinding the phenomenon described above, the inventors have newly foundthat such a significant decrease in resistance value can be prevented byusing a magnetic tape which will be described later as the magnetictape.

One aspect of the invention has been completed based on the findingdescribed above.

That is, according to one aspect of the invention, there is provided amagnetic tape device comprising: a magnetic tape; and a reproducinghead, in which the reproducing head is a magnetic head (hereinafter,also referred to as a “TMR head”) including a tunnel magnetoresistanceeffect type element (hereinafter, also referred to as a “TMR element”)as a reproducing element, the magnetic tape includes a non-magneticsupport, and a magnetic layer including ferromagnetic powder, a bindingagent, and fatty acid ester on the non-magnetic support, a full width athalf maximum of spacing distribution measured by optical interferometryregarding a surface of the magnetic layer before performing a vacuumheating with respect to the magnetic tape (hereinafter, also referred toas “FWHM_(before)”) is greater than 0 nm and equal to or smaller than7.0 nm, a full width at half maximum of spacing distribution measured byoptical interferometry regarding the surface of the magnetic layer afterperforming the vacuum heating with respect to the magnetic tape(hereinafter, also referred to as “FWHM_(after)”) is greater than 0 nmand equal to or smaller than 7.0 nm, and a difference(S_(after)−S_(before)) between a spacing S_(after) measured by opticalinterferometry regarding the surface of the magnetic layer afterperforming the vacuum heating with respect to the magnetic tape and aspacing S_(before) measured by optical interferometry regarding thesurface of the magnetic layer before performing the vacuum heating withrespect to the magnetic tape (hereinafter, also simply referred to as a“difference (S_(after)−S_(before))”) is greater than 0 nm and equal toor smaller than 9.0 nm.

According to another aspect of the invention, there is provided amagnetic reproducing method comprising: reproducing information recordedon a magnetic tape by a reproducing head, in which the reproducing headis a magnetic head including a tunnel magnetoresistance effect typeelement as a reproducing element, the magnetic tape includes anon-magnetic support, and a magnetic layer including ferromagneticpowder, a binding agent, and fatty acid ester on the non-magneticsupport, a full width at half maximum of spacing distribution measuredby optical interferometry regarding a surface of the magnetic layerbefore performing a vacuum heating with respect to the magnetic tape isgreater than 0 nm and equal to or smaller than 7.0 nm, a full width athalf maximum of spacing distribution measured by optical interferometryregarding the surface of the magnetic layer after performing the vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 7.0 nm, and a difference (S_(after)−S_(before))between a spacing S_(after) measured by optical interferometry regardingthe surface of the magnetic layer after performing the vacuum heatingwith respect to the magnetic tape and a spacing S_(before) measured byoptical interferometry regarding the surface of the magnetic layerbefore performing the vacuum heating with respect to the magnetic tapeis greater than 0 nm and equal to or smaller than 9.0 nm.

In the invention and the specification, the “vacuum heating” of themagnetic tape is performed by holding the magnetic tape in anenvironment of a pressure of 200 Pa to 0.01 MPa and at an atmospheretemperature of 70° C. to 90° C. for 24 hours.

In the invention and the specification, the spacing measured by opticalinterferometry regarding the surface of the magnetic layer of themagnetic tape is a value measured by the following method. In theinvention and the specification, the “surface of the magnetic layer” ofthe magnetic tape is identical to the surface of the magnetic tape onthe magnetic layer side.

In a state where the magnetic tape and a transparent plate-shaped member(for example, glass plate or the like) are overlapped onto each other sothat the surface of the magnetic layer of the magnetic tape faces thetransparent plate-shaped member, a pressing member is pressed againstthe side of the magnetic tape opposite to the magnetic layer side at apressure of 5.05×10⁴ N/m (0.5 atm). In this state, the surface of themagnetic layer of the magnetic tape is irradiated with light through thetransparent plate-shaped member (irradiation region: 150,000 to 200,000μm²), and a spacing (distance) between the surface of the magnetic layerof the magnetic tape and the surface of the transparent plate-shapedmember on the magnetic tape side is acquired based on intensity (forexample, contrast of interference fringe image) of interference lightgenerated due to a difference in a light path between reflected lightfrom the surface of the magnetic layer of the magnetic tape andreflected light from the surface of the transparent plate-shaped memberon the magnetic tape side. The light emitted here is not particularlylimited. In a case where the emitted light is light having an emissionwavelength over a comparatively wide wavelength range as white lightincluding light having a plurality of wavelengths, a member having afunction of selectively cutting light having a specific wavelength or awavelength other than wavelengths in a specific wavelength range, suchas an interference filter, is disposed between the transparentplate-shaped member and a light reception unit which receives reflectedlight, and light at some wavelengths or in some wavelength ranges of thereflected light is selectively incident to the light reception unit. Ina case where the light emitted is light (so-called monochromatic light)having a single luminescence peak, the member described above may not beused. The wavelength of light incident to the light reception unit canbe set to be 500 to 700 nm, for example. However, the wavelength oflight incident to the light reception unit is not limited to be in therange described above. In addition, the transparent plate-shaped membermay be a member having transparency through which emitted light passes,to the extent that the magnetic tape is irradiated with light throughthis member and interference light is obtained.

The measurement described above can be performed by using a commerciallyavailable tape spacing analyzer (TSA) such as Tape Spacing Analyzermanufactured by Micro Physics, Inc., for example. The spacingmeasurement of the examples was performed by using Tape Spacing Analyzermanufactured by Micro Physics, Inc.

In addition, the full width at half maximum of spacing distribution ofthe invention and the specification is a full width at half maximum(FWHM), in a case where the interference fringe image obtained by themeasurement of the spacing described above is divided into 300,000points, a spacing of each point (distance between the surface of themagnetic layer of the magnetic tape and the surface of the transparentplate-shaped member on the magnetic tape side) is acquired, this spacingis shown with a histogram, and this histogram is fit with Gaussiandistribution.

Further, the difference (S_(after)−S_(before)) is a value obtained bysubtracting a mode before the vacuum heating from a mode after thevacuum heating of the 300,000 points.

One aspect of the magnetic tape device and the magnetic reproducingmethod is as follows.

In one aspect, the FWHM_(before) is 3.0 nm to 7.0 nm.

In one aspect, the FWHM_(after) is 3.0 nm to 7.0 nm.

In one aspect, the difference (S_(after)−S_(before)) is 2.0 nm to 9.0nm.

In one aspect, a center line average surface roughness Ra measuredregarding a surface of the magnetic layer is equal to or smaller than2.8 nm.

In one aspect, the center line average surface roughness Ra is equal toor smaller than 2.5 nm.

In one aspect, the magnetic tape includes a non-magnetic layer includingnon-magnetic powder and a binding agent between the non-magnetic supportand the magnetic layer, and a total thickness of the magnetic layer andthe non-magnetic layer is equal to or smaller than 1.8 μm.

In one aspect, the total thickness of the magnetic layer and thenon-magnetic layer is equal to or smaller than 1.1 μm.

According to one aspect of the invention, it is possible to preventoccurrence of a significant decrease in resistance value in the TMRhead, in a case of reproducing information recorded on the magnetic tapeby the TMR head.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic configuration diagram of a vibration impartingdevice used in examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape Device

One aspect of the invention relates to a magnetic tape device including:a magnetic tape; and a reproducing head, in which the reproducing headis a magnetic head including a tunnel magnetoresistance effect typeelement as a reproducing element, the magnetic tape includes anon-magnetic support, and a magnetic layer including ferromagneticpowder, a binding agent, and fatty acid ester on the non-magneticsupport, a full width at half maximum of spacing distribution measuredby optical interferometry regarding the surface of the magnetic layerbefore performing a vacuum heating with respect to the magnetic tape(FWHM_(before)) is greater than 0 nm and equal to or smaller than 7.0nm, a full width at half maximum of spacing distribution measured byoptical interferometry regarding the surface of the magnetic layer afterperforming the vacuum heating with respect to the magnetic tape(FWHM_(after)) is greater than 0 nm and equal to or smaller than 7.0 nm,and a difference (S_(after)−S_(before)) between a spacing S_(after)measured by optical interferometry regarding the surface of the magneticlayer after performing the vacuum heating with respect to the magnetictape and a spacing S_(before) measured by optical interferometryregarding the surface of the magnetic layer before performing the vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 9.0 nm.

In the magnetic tape device, in a case of using a magnetic tape of therelated art, in a case of using a TMR head as a reproducing head, aphenomenon in which a resistance value (electric resistance)significantly decreases in the TMR head occurs. This phenomenon is aphenomenon that has been newly found by the inventors. The inventorshave considered the reason for the occurrence of such a phenomenon is asfollows.

The TMR head is a magnetic head using a tunnel magnetoresistance effectand includes two electrodes with an insulating layer (tunnel barrierlayer) interposed therebetween. The tunnel barrier layer positionedbetween the two electrodes is an insulating layer, and thus, even in acase where a voltage is applied between the two electrodes, in general,a current does not flow or does not substantially flow between theelectrodes. However, a current (tunnel current) flows by a tunnel effectdepending on a direction of a magnetic field of a free layer affected bya leakage magnetic field from the magnetic tape, and a change in amountof a tunnel current flow is detected as a change in resistance value bythe tunnel magnetoresistance effect. By converting the change inresistance value into a change in voltage, information recorded on themagnetic tape can be reproduced.

Examples of a structure of the MR head include a current-in-plane (CIP)structure and a current-perpendicular-to-plane (CPP) structure, and theTMR head is a magnetic head having a CPP structure. In the MR headhaving a CPP structure, a current flows in a direction perpendicular toa film surface of an MR element, that is, a direction in which themagnetic tape is transported, in a case of reproducing informationrecorded on the magnetic tape. With respect to this, other MR heads, forexample, a spin valve type GMR head which is widely used in recent yearsamong the GMR heads has a CIP structure. In the MR head having a CIPstructure, a current flows in a direction in a film plane of an MRelement, that is, a direction perpendicular to a direction in which themagnetic tape is transported, in a case of reproducing informationrecorded on the magnetic tape.

As described above, the TMR head has a special structure which is notapplied to other MR heads which are currently practically used.Accordingly, in a case where short circuit (bypass due to damage) occurseven at one portion between the two electrodes, the resistance valuesignificantly decreases. A significant decrease in resistance value in acase of the short circuit occurring even at one portion between the twoelectrodes as described above is a phenomenon which does not occur inother MR heads. In the magnetic disk device using a levitation typerecording and reproducing system, a magnetic disk and a reproducing headdo not come into contact with each other at the time of reproducing, andthus, damage causing short circuit hardly occurs. On the other hand, inthe magnetic tape using a sliding type recording and reproducing system,in a case where any measures are not prepared, the TMR head is damageddue to the sliding between the TMR head and the magnetic tape, and thus,short circuit easily occurs. The inventors have assumed that this is thereason why a decrease in resistance value of the TMR head significantlyoccurs at the time of reproducing, in a case of using the TMR head asthe reproducing head in the magenta tape device.

With respect to this, as a result of intensive studies of the inventors,the inventors have newly found that it is possible to prevent aphenomenon in which a decrease in resistance value of the TMR headsignificantly occurs at the time of reproducing, in a case of using theTMR head as the reproducing head in the magenta tape device, by usingthe magnetic tape in which the FWHM_(before), the FWHM_(after), and thedifference (S_(after)−S_(before)) are respectively in the rangesdescribed above. The surmise of the inventors regarding this point is asdescribed in the following (1) and (2).

(1) A portion (projection) which mainly comes into contact (so-calledreal contact) with the reproducing head in a case where the magnetictape and the reproducing head slide on each other, and a portion(hereinafter, referred to as a “base portion”) having a height lowerthan that of the portion described above are normally present on thesurface of the magnetic layer. The inventors have thought that thespacing described above is a value which is an index of a distancebetween the reproducing head and the base portion in a case where themagnetic tape and the reproducing head slide on each other. However, itis thought that, in a case where a lubricant included in the magneticlayer forms a liquid film on the surface of the magnetic layer, theliquid film is present between the base portion and the reproducinghead, and thus, the spacing is narrowed by the thickness of the liquidfilm.

Meanwhile, the lubricant is generally divided broadly into a fluidlubricant and a boundary lubricant. Fatty acid ester included in themagnetic layer of the magnetic tape is known as a component which canfunction as a liquid lubricant. It is considered that a fluid lubricantcan protect the surface of the magnetic layer by forming a liquid filmon the surface of the magnetic layer. The inventors have thought thatthe presence of the liquid film of fatty acid ester on the surface ofthe magnetic layer contributes to smooth sliding (improvement of slidingproperties) between the magnetic tape and the reproducing head (TMRhead).

However, an excessive amount of fatty acid ester present on the surfaceof the magnetic layer causes sticking due to the formation of a meniscus(liquid crosslinking) between the surface of the magnetic layer and thereproducing head due to fatty acid ester, thereby decreasing slidingproperties.

In regards to this point, the inventors focused on the idea that fattyacid ester is a component having properties of volatilizing by vacuumheating, and the difference (S_(after)−S_(before)) of a spacing betweena state after the vacuum heating (state in which a liquid film of fattyacid ester is volatilized and removed) and a state before the vacuumheating (state in which the liquid film of fatty acid ester is present)was used as an index for the thickness of the liquid film formed offatty acid ester on the surface of the magnetic layer. The inventorshave surmised that the presence of the liquid film of fatty acid esteron the surface of the magnetic layer, so that the value of thedifference is greater than 0 nm and equal to or smaller than 9.0 nm,causes the improvement of sliding properties between the reproducinghead (TMR head) and the magnetic tape while preventing sticking.

(2) A smaller value of the full width at half maximum of spacingdistribution means that a variation in the values of the spacingmeasured on each part of the surface of the magnetic layer is small. Asa result of intensive studies, the inventors found that it is effectiveto increase uniformity of a contact state between the surface of themagnetic layer and the reproducing head by increasing uniformity of aheight of projection present on the surface of the magnetic layer andincreasing uniformity of a thickness of a liquid film of fatty acidester, in order to realize smooth sliding between the magnetic tape andthe reproducing head.

In regards to this point, it is considered that the reason for thevariation in values of the spacing is a variation in height of theprojection of the surface of the magnetic layer and a variation in thethickness of the liquid film fatty acid ester. The inventors havesurmised that the full width at half maximum of the spacing distributionFWHM_(before) measured before the vacuum heating, that is, in a statewhere the liquid film of fatty acid ester is present on the surface ofthe magnetic layer, becomes great, as the variation in height of theprojection and the variation in the thickness of the liquid film offatty acid ester are great. Particularly, the spacing distributionFWHM_(before) is greatly affected by the variation in the thickness ofthe liquid film of fatty acid ester. In contrast, the inventors havesurmised that the full width at half maximum of the spacing distributionFWHM_(after) measured after the vacuum heating, that is, in a statewhere the liquid film of fatty acid ester is removed from the surface ofthe magnetic layer, becomes great, as the variation in height of theprojection is great. That is, the inventors have surmised that smallfull widths at half maximum of spacing distributions FWHM_(before) andFWHM_(after) mean a small variation in the thickness of the liquid filmof fatty acid ester on the surface of the magnetic layer and a smallvariation in height of the projection. It was clear that it is possibleto prevent a phenomenon in which a decrease in resistance value of theTMR head significantly occurs at the time of reproducing, in a case ofusing the TMR head as the reproducing head in the magnetic tape device,by increasing the uniformity of the height of the projection and thethickness of the liquid film of fatty acid ester so that the full widthsat half maximum of the spacing distribution FWHM_(before) andFWHM_(after) are greater than 0 nm and equal to or smaller than 7.0 nm.

However, the above-mentioned description includes the surmise of theinventors. The invention is not limited to such a surmise.

Hereinafter, the magnetic tape device will be described morespecifically. A “decrease in resistance value of the TMR head” describedbelow is a significant decrease in resistance value of the TMR headoccurring in a case of reproducing information recorded on the magnetictape by the TMR head, in the magnetic tape device in which the TMR headis mounted as the reproducing head, unless otherwise noted.

Magnetic Tape

Full Width at Half Maximum of Spacing Distribution FWHM_(before) andFWHM_(after) Both of the full width at half maximum of spacingdistribution FWHM_(before) before the vacuum heating and the full widthat half maximum of spacing distribution FWHM_(after) after the vacuumheating which are measured in the magnetic tape are greater than 0 nmand equal to or smaller than 7.0 nm. The inventors have surmised thatthis point contributes to the prevention of a decrease in resistancevalue of the TMR head. From a viewpoint of further preventing a decreasein resistance value of the TMR head, the FWHM_(before) and theFWHM_(after) are preferably equal to or smaller than 6.5 nm, morepreferably equal to or smaller than 6.0 nm, even more preferably equalto or smaller than 5.5 nm, still more preferably equal to or smallerthan 5.0 nm, and still even more preferably equal to or smaller than 4.5nm. The FWHM_(before) and the FWHM_(after) can be, for example, equal toor greater than 0.5 nm, equal to or greater than 1.0 nm, equal to orgreater than 2.0 nm, or equal to or greater than 3.0 nm. Meanwhile, froma viewpoint of preventing a decrease in resistance value of the TMRhead, it is preferable that the values thereof are small, and therefore,the values thereof may be smaller than the exemplified values.

The full width at half maximum of spacing distribution FWHM_(before)before the vacuum heating can be decreased mainly by decreasing thevariation in the thickness of the liquid film of fatty acid ester. Anexample of a specific method will be described later. Meanwhile, thefull width at half maximum of spacing distribution FWHM_(after) afterthe vacuum heating can be decreased by decreasing the variation inheight of the projection of the surface of the magnetic layer. In orderto realize the decrease described above, it is preferable that apresence state of the powder component included in the magnetic layer,for example, non-magnetic filler, which will be described laterspecifically, in the magnetic layer is controlled. An example of aspecific method will be described later.

Difference (S_(after)−S_(before))

The difference (S_(after)−S_(before)) of the spacings before and afterthe vacuum heating measured in the magnetic tape is greater than 0 nmand equal to or smaller than 9.0 nm. The inventors have surmised thatthis point also contributes to the prevention of a decrease inresistance value of the TMR head. From a viewpoint of further preventinga decrease in resistance value of the TMR head, the difference(S_(after)−S_(before)) is preferably equal to or greater than 0.1 nm,more preferably equal to or greater than 1.0 nm, even more preferablyequal to or greater than 1.5 nm, still more preferably equal to orgreater than 2.0 nm, and still even more preferably equal to or greaterthan 2.5 nm. Meanwhile, from a viewpoint of further preventing adecrease in resistance value of the TMR head, the difference(S_(after)−S_(before)) is preferably equal to or smaller than 8.5 nm,more preferably equal to or smaller than 8.0 nm, even more preferablyequal to or smaller than 7.0 nm, still preferably equal to or smallerthan 6.0 nm, still more preferably equal to or smaller than 5.0 nm,still even more preferably equal to or smaller than 4.0 nm, and stillfurther more preferably equal to or smaller than 3.0 nm. The difference(S_(after)−S_(before)) can be controlled by the amount of fatty acidester added to a magnetic layer forming composition. In addition,regarding the magnetic tape including a non-magnetic layer between thenon-magnetic support and the magnetic layer, the difference(S_(after)−S_(before)) can also be controlled by the amount of fattyacid ester added to a non-magnetic layer forming composition. This isbecause that the non-magnetic layer can play a role of holding alubricant and supplying the lubricant to the magnetic layer, and fattyacid ester included in the non-magnetic layer may be moved to themagnetic layer and present in the surface of the magnetic layer.

Next, the magnetic layer and the like included in the magnetic tape willbe described more specifically.

Magnetic Layer

Fatty Acid Ester

The magnetic tape includes fatty acid ester in the magnetic layer. Thefatty acid ester may be included alone as one type or two or more typesthereof may be included.

Examples of fatty acid ester include esters of lauric acid, myristicacid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenicacid, behenic acid, erucic acid, and elaidic acid. Specific examplesthereof include butyl myristate, butyl palmitate, butyl stearate (butylstearate), neopentyl glycol dioleate, sorbitan monostearate, sorbitandistearate, sorbitan tristearate, oleyl oleate, isocetyl stearate,isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate,and butoxyethyl stearate.

The content of fatty acid ester, as the content of the magnetic layerforming composition, is, for example, 0.1 to 10.0 parts by mass and ispreferably 1.0 to 7.0 parts by mass with respect to 100.0 parts by massof ferromagnetic powder. In a case of using two or more kinds ofdifferent fatty acid esters as the fatty acid ester, the content thereofis the total content thereof. In the invention and the specification,the same applies to content of other components, unless otherwise noted.In addition, in the invention and the specification, a given componentmay be used alone or used in combination of two or more kinds thereof,unless otherwise noted.

In a case where the magnetic tape includes a non-magnetic layer betweenthe non-magnetic support and the magnetic layer, the content of fattyacid ester in a non-magnetic layer forming composition is, for example,0 to 10.0 parts by mass and is preferably 0.1 to 8.0 parts by mass withrespect to 100.0 parts by mass of non-magnetic powder.

Other Lubricants

The magnetic tape includes fatty acid ester which is one kind oflubricants at least in the magnetic layer. The lubricants other thanfatty acid ester may be arbitrarily included in the magnetic layerand/or the non-magnetic layer. As described above, the lubricantincluded in the non-magnetic layer may be moved to the magnetic layerand present in the surface of the magnetic layer. As the lubricant whichmay be arbitrarily included, fatty acid can be used. In addition, fattyacid amide and the like can also be used. Fatty acid ester is known as acomponent which can function as a fluid lubricant, whereas fatty acidand fatty acid amide are known as a component which can function as aboundary lubricant. It is considered that the boundary lubricant is alubricant which can be adsorbed to a surface of powder (for example,ferromagnetic powder) and form a rigid lubricant film to decreasecontact friction.

Examples of fatty acid include lauric acid, myristic acid, palmiticacid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenicacid, erucic acid, and elaidic acid, and stearic acid, myristic acid,and palmitic acid are preferable, and stearic acid is more preferable.Fatty acid may be included in the magnetic layer in a state of salt suchas metal salt.

As fatty acid amide, amide of various fatty acid described above isused, and examples thereof include lauric acid amide, myristic acidamide, palmitic acid amide, and stearic acid amide.

Regarding fatty acid and a derivative of fatty acid (amide and ester), apart derived from fatty acid of the fatty acid derivative preferably hasa structure which is the same as or similar to that of fatty acid usedin combination. As an example, in a case of using stearic acid as fattyacid, it is preferable to use stearic acid ester and/or stearic acidamide.

The content of fatty acid in the magnetic layer forming composition is,for example, 0 to 10.0 parts by mass, preferably 0.1 to 10.0 parts bymass, and more preferably 1.0 to 7.0 parts by mass, with respect to100.0 parts by mass of the ferromagnetic powder. The content of fattyacid amide in the magnetic layer forming composition is, for example, 0to 3.0 parts by mass, preferably 0 to 2.0 parts by mass, and morepreferably 0 to 1.0 part by mass with respect to 100.0 parts by mass ofthe ferromagnetic powder.

In a case where the magnetic tape includes a non-magnetic layer betweenthe non-magnetic support and the magnetic layer, the content of fattyacid in the non-magnetic layer forming composition is, for example, 0 to10.0 parts by mass, preferably 1.0 to 10.0 parts by mass, and morepreferably 1.0 to 7.0 parts by mass with respect to 100.0 parts by massof the non-magnetic powder. The content of fatty acid amide in thenon-magnetic layer forming composition is, for example, 0 to 3.0 partsby mass and preferably 0 to 1.0 part by mass with respect to 100.0 partsby mass of the non-magnetic powder.

Ferromagnetic Powder

As the ferromagnetic powder included in the magnetic layer,ferromagnetic powder normally used in the magnetic layer of variousmagnetic recording media can be used. It is preferable to useferromagnetic powder having a small average particle size, from aviewpoint of improvement of recording density of the magnetic tape. Fromthis viewpoint, ferromagnetic powder having an average particle sizeequal to or smaller than 50 nm is preferably used as the ferromagneticpowder. Meanwhile, the average particle size of the ferromagnetic powderis preferably equal to or greater than 10 nm, from a viewpoint ofstability of magnetization.

As a preferred specific example of the ferromagnetic powder,ferromagnetic hexagonal ferrite powder can be used. An average particlesize of the ferromagnetic hexagonal ferrite powder is preferably 10 nmto 50 nm and more preferably 20 nm to 50 nm, from a viewpoint ofimprovement of recording density and stability of magnetization. Fordetails of the ferromagnetic hexagonal ferrite powder, descriptionsdisclosed in paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134to 0136 of JP2011-216149A, and paragraphs 0013 to 0030 of JP2012-204726Acan be referred to, for example.

As a preferred specific example of the ferromagnetic powder,ferromagnetic metal powder can also be used. An average particle size ofthe ferromagnetic metal powder is preferably 10 nm to 50 nm and morepreferably 20 nm to 50 nm, from a viewpoint of improvement of recordingdensity and stability of magnetization. For details of the ferromagneticmetal powder, descriptions disclosed in paragraphs 0137 to 0141 ofJP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351 can bereferred to, for example.

In the invention and the specification, average particle sizes ofvarious powder such as the ferromagnetic powder and the like are valuesmeasured by the following method with a transmission electronmicroscope, unless otherwise noted.

The powder is imaged at a magnification ratio of 100,000 with atransmission electron microscope, the image is printed on printing paperso that the total magnification of 500,000 to obtain an image ofparticles configuring the powder. A target particle is selected from theobtained image of particles, an outline of the particle is traced with adigitizer, and a size of the particle (primary particle) is measured.The primary particle is an independent particle which is not aggregated.

The measurement described above is performed regarding 500 particlesarbitrarily extracted. An arithmetical mean of the particle size of 500particles obtained as described above is an average particle size of thepowder. As the transmission electron microscope, a transmission electronmicroscope H-9000 manufactured by Hitachi, Ltd. can be used, forexample. In addition, the measurement of the particle size can beperformed by well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss.

In the invention and the specification, the average particle size of theferromagnetic powder and other powder is an average particle sizeobtained by the method described above, unless otherwise noted. Theaverage particle size shown in examples which will be described later isa value measured by using transmission electron microscope H-9000manufactured by Hitachi, Ltd. as the transmission electron microscope,and image analysis software KS-400 manufactured by Carl Zeiss as theimage analysis software, unless otherwise noted. In the invention andthe specification, the powder means an aggregate of a plurality ofparticles. For example, the ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. The aggregate of the plurality ofparticles not only includes an aspect in which particles configuring theaggregate directly come into contact with each other, and also includesan aspect in which a binding agent or an additive which will bedescribed later is interposed between the particles. A term “particles”is also used for describing the powder.

As a method of collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted, (1) in acase where the shape of the particle observed in the particle imagedescribed above is a needle shape, a fusiform shape, or a columnar shape(here, a height is greater than a maximum long diameter of a bottomsurface), the size (particle size) of the particles configuring thepowder is shown as a length of a long axis configuring the particle,that is, a long axis length, (2) in a case where the shape of theparticle is a planar shape or a columnar shape (here, a thickness or aheight is smaller than a maximum long diameter of a plate surface or abottom surface), the particle size is shown as a maximum long diameterof the plate surface or the bottom surface, and (3) in a case where theshape of the particle is a sphere shape, a polyhedron shape, or anunspecified shape, and the long axis configuring the particles cannot bespecified from the shape, the particle size is shown as an equivalentcircle diameter. The equivalent circle diameter is a value obtained by acircle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a short axis, that is, a short axis length of the particles ismeasured in the measurement described above, a value of (long axislength/short axis length) of each particle is obtained, and anarithmetical mean of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the shortaxis length as the definition of the particle size is a length of ashort axis configuring the particle, in a case of (2), the short axislength is a thickness or a height, and in a case of (3), the long axisand the short axis are not distinguished, thus, the value of (long axislength/short axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average long axislength, in a case of the definition (2), the average particle size is anaverage plate diameter, and an average plate ratio is an arithmeticalmean of (maximum long diameter/thickness or height). In a case of thedefinition (3), the average particle size is an average diameter (alsoreferred to as an average particle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably 50 to 90 mass % and more preferably 60 to90 mass %. The components other than the ferromagnetic powder of themagnetic layer are at least a binding agent and fatty acid ester, andone or more kinds of additives may be arbitrarily included. A highfilling percentage of the ferromagnetic powder in the magnetic layer ispreferable from a viewpoint of improvement in the recording density.

Binding Agent

The magnetic tape includes a binding agent in the magnetic layertogether with the ferromagnetic powder and fatty acid ester. The bindingagent is one or more kinds of resin. As the binding agent, a resinselected from a polyurethane resin, a polyester resin, a polyamideresin, a vinyl chloride resin, an acrylic resin obtained bycopolymerizing styrene, acrylonitrile, or methyl methacrylate, acellulose resin such as nitrocellulose, an epoxy resin, a phenoxy resin,and a polyvinylalkylal resin such as polyvinyl acetal or polyvinylbutyral can be used alone or a plurality of resins can be mixed witheach other to be used. Among these, a polyurethane resin, an acrylicresin, a cellulose resin, and a vinyl chloride resin are preferable.These resins may be a homopolymer or a copolymer. These resins can beused as the binding agent even in the non-magnetic layer and/or a backcoating layer which will be described later. For the binding agentdescribed above, description disclosed in paragraphs 0028 to 0031 ofJP2010-24113A can be referred to. In addition, the binding agent may bea radiation curable resin such as an electron beam-curable resin. Forthe radiation curable resin, descriptions disclosed in paragraphs 0044and 0045 of JP2011-048878A can be referred to.

In addition, a curing agent can be used together with a resin which canbe used as the binding agent. The curing agent is a compound includingat least one and preferably two or more crosslinking functional groupsin one molecule. As the curing agent, polyisocyanate is suitable. Forthe details of polyisocyanate, descriptions disclosed in paragraphs 0124and 0125 of JP2011-216149A can be referred to. The amount of the curingagent used can be, for example, 0 to 80.0 parts by mass with respect to100.0 parts by mass of the binding agent, and is preferably 50.0 to 80.0parts by mass, from a viewpoint of improvement in strength of each layersuch as the magnetic layer.

Other Components

Additives can be added to the magnetic layer, if necessary. It ispreferable that the magnetic layer includes one or more kinds of thenon-magnetic filler. The non-magnetic filler is identical to thenon-magnetic powder. As the non-magnetic filler, a non-magnetic filler(hereinafter, also referred to as a “projection formation agent”) whichis added for controlling the projection of the surface of the magnetictape and a non-magnetic filler (hereinafter, referred to as an“abrasive”) which is added as an abrasive imparting abrasive propertiesto the surface of the magnetic tape are mainly used. The magnetic layerpreferably includes at least the projection formation agent and morepreferably includes the projection formation agent and the abrasive.

The projection formation agent may be powder of inorganic substances(inorganic powder) or powder of organic substances (organic powder), andis preferably powder of inorganic substances. In addition, carbon blackis also preferable. An average particle size of carbon black ispreferably equal to or greater than 20 nm and more preferably equal toor greater than 30 nm. In addition, the average particle size of carbonblack is preferably equal to or smaller than 150 nm and more preferablyequal to or smaller than 100 nm.

Examples of the inorganic powder include powder of inorganic oxide suchas metal oxide, metal carbonate, metal sulfate, metal nitride, metalcarbide, and metal sulfide, and specific examples thereof include powderof α-alumina, β-alumina, γ-alumina, θ-alumina, silicon oxide such assilicon dioxide, silicon carbide, chromium oxide, cerium oxide, α-ironoxide, goethite, corundum, silicon nitride, titanium carbide, titaniumdioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide,boron nitride, zinc oxide, calcium carbonate, calcium sulfate, bariumsulfate, and molybdenum disulfide, or composite inorganic powderincluding two or more kinds thereof. The inorganic oxide powder is morepreferable and silicon oxide powder is even more preferable.

The projection formation agent preferably has uniformity of the particlesize, from a viewpoint of further improving electromagnetic conversioncharacteristics. From a viewpoint of availability of particles havinghigh uniformity of the particle size, the projection formation agent ispreferably colloidal particles. In the invention and the specification,the “colloidal particles” are particles which are not precipitated anddispersed to generate a colloidal dispersion, in a case where 1 g of theparticles is added to 100 mL of at least one organic solvent of at leastmethyl ethyl ketone, cyclohexanone, toluene, or ethyl acetate, or amixed solvent including two or more kinds of the solvent described aboveat an arbitrary mixing ratio. The average particle size of the colloidalparticles is a value obtained by a method disclosed in a paragraph 0015of JP2011-048878A as a measurement method of an average particlediameter. In a case where the non-magnetic filler used in the formationof the magnetic layer is available, it is possible to determine whetheror not the non-magnetic filler included in the magnetic layer iscolloidal particles, by evaluating whether or not such a non-magneticfiller has properties which are the properties of the colloidalparticles described above. Alternatively, the determination can also beperformed by evaluating whether or not the non-magnetic filler extractedfrom the magnetic layer has properties which are the properties of thecolloidal particles described above. The extraction of the non-magneticfiller from the magnetic layer can be performed by the following method,for example.

1. 1 g of the magnetic layer is scraped off. The scraping can beperformed, for example, by a razor blade.

2. A magnetic layer sample obtained by the scraping is put in a vesselsuch as an eggplant flask and 100 ml of tetrahydrofuran is added intothis vessel. Examples of tetrahydrofuran include commercially availabletetrahydrofuran to which a stabilizer is added and commerciallyavailable tetrahydrofuran to which a stabilizer is not added. Meanwhile,here, the commercially available tetrahydrofuran to which a stabilizeris not added is used. The same applies to tetrahydrofuran used inwashing described hereinafter.

3. A circulation tube is attached to the vessel and heated in a waterbath at a water temperature of 60° C. for 90 minutes. After filteringthe content in the heated vessel with a filter paper, the solid contentremaining on the filter paper is washed with tetrahydrofuran severaltimes, and the washed solid content is moved to a vessel such as abeaker. A 4 N (4 mol/L) hydrochloric acid aqueous solution is added intothis vessel and a residue remaining without being dissolved is extractedby filtering. As a filter, a filter having a hole diameter smaller than0.05 μm is used. For example, a membrane filter used for chromatographyanalysis (for example, MF Millipore manufactured by Merck MilliporeCorporation) can be used. The residue extracted by the filtering iswashed with pure water several times and dried.

Ferromagnetic powder and organic matters (binding agent and the like)are dissolved by the operation described above, and a non-magneticfiller is collected as a residue.

By performing the steps described above, the non-magnetic filler can beextracted from the magnetic layer. In a case where a plurality of kindsof non-magnetic fillers are included in the non-magnetic fillerextracted as described above, the plurality of kinds of non-magneticfillers can be divided depending on the differences of density.

As preferred colloidal particles, inorganic oxide colloidal particlescan be used. As the inorganic oxide colloidal particles, colloidalparticles of inorganic oxide described above can be used, and compositeinorganic oxide colloidal particles such as SiO₂—Al₂O₃, SiO₂—B₂O₃,TiO₂.CeO₂, SnO₂—Sb₂O₃, SiO₂—Al₂O₃.TiO₂, and TiO₂.CeO₂.SiO₂ can be used.The inorganic oxide colloidal particles such as SiO₂, Al₂O₃, TiO₂, ZrO₂,and Fe₂O₃ are preferable and silica colloidal particles (colloidalsilica) are particularly preferable. Meanwhile, typical colloidalparticles have a hydrophilic surface, and thus, the colloidal particlesare suitable for manufacturing a colloidal solution using water as adispersion medium. For example, colloidal silica obtained by a generalsynthesis method has a surface covered with polarized oxygen atoms(O²⁻), and thus, colloidal silica adsorbs water in water, forms ahydroxyl group, and is stabilized. However, these particles are hardlypresent in a colloidal state, in an organic solvent normally used in themagnetic layer forming composition. With respect to this, the colloidalparticles of the invention and the specification are particles which arenot precipitated but are dispersed to cause a colloidal dispersion, when1 g thereof is added with respect to 100 mL of the organic solventdescribed above. Such colloidal particles can be prepared by awell-known method of hydrophobing the surface by surface treatment. Fordetails of such hydrophobization treatment, descriptions disclosed inJP1993-269365A (JP-H05-269365A), JP1993-287213A (JP-H05-287213A), andJP2007-63117A are referred to.

As a manufacturing method of the silica colloidal particles (colloidalsilica) which are preferred colloidal particles, two kinds of methodssuch as a water glass method and a sol-gel method are generally known.The water glass method is a method of using silica soda (sodiumsilicate, so-called water glass) as a raw material, performing ionexchange with respect to this to generate an active silica, and causingparticle growth. Meanwhile, the sol-gel method is a method of usingtetraalkoxysilane as a raw material, and performing hydrolysis under abasic catalyst and causing particle growth at the same time. In a caseof using the silica colloidal particles as the non-magnetic particles,the silica colloidal particles may be manufactured by any manufacturingmethod described above.

An average particle size of the projection formation agent is preferably50 to 200 nm, and more preferably 50 to 150 nm.

The content of the projection formation agent in the magnetic layer ispreferably 1.0 to 4.0 parts by mass and more preferably 1.5 to 3.5 partsby mass with respect to 100.0 parts by mass of the ferromagnetic powder.

Meanwhile, the abrasive may be inorganic powder or organic powder, andthe inorganic powder is preferable. Examples of the abrasive includepowders of alumina (Al₂O₃), silicon carbide, boron carbide (B₄C), SiO₂,TiC, chromium oxide (Cr₂O₃), cerium oxide, zirconium oxide (ZrO₂), ironoxide, diamond, and the like which are materials normally used as theabrasive of the magnetic layer, and among these, alumina powder such asca-alumina and silicon carbide powder are preferable. The content of theabrasive in the magnetic layer is preferably 1.0 to 20.0 parts by mass,more preferably 3.0 to 15.0 parts by mass, and even more preferably 4.0to 10.0 parts by mass with respect to 100.0 parts by mass of theferromagnetic powder. The average particle size of the abrasive is, forexample, 30 to 300 nm and preferably 50 to 200 nm.

An arbitrary amount of one or more kinds of various additives such as adispersing agent, a dispersing assistant, an antifungal agent, anantistatic agent, an antioxidant, and carbon black may be further addedto the magnetic layer. As the additives, commercially available productscan be suitably selectively used according to the desired properties.Alternatively, a compound synthesized by a well-known method can be usedas the additives.

Center Line Average Surface Roughness Ra Measured Regarding Surface ofMagnetic Layer

Increasing a surface smoothness of the magnetic layer in the magnetictape causes improvement of electromagnetic conversion characteristics.Regarding the surface smoothness of the magnetic layer, the center lineaverage surface roughness Ra measured regarding the surface of themagnetic layer can be an index. In the invention and the specification,the center line average surface roughness Ra measured regarding thesurface of the magnetic layer of the magnetic tape is a value measuredwith an atomic force microscope (AFM) in a region having an area of 40μm×40 μm. As an example of the measurement conditions, the followingmeasurement conditions can be used. The center line average surfaceroughness Ra shown in examples which will be described later is a valueobtained by the measurement under the following measurement conditions.

The measurement is performed regarding the region of 40 μm×40 μm of thearea of the surface of the magnetic layer of the magnetic tape with anAFM (Nanoscope 4 manufactured by Veeco Instruments, Inc.). A scan speed(probe movement speed) is set as 40 μm/sec and a resolution is set as512 pixel×512 pixel.

In one aspect, the center line average surface roughness Ra measuredregarding the surface of the magnetic layer of the magnetic tape ispreferably equal to or smaller than 2.8 nm, more preferably equal to orsmaller than 2.5 nm, even more preferably equal to or smaller than 2.3nm, and still more preferably equal to or smaller than 2.0 nm, from aviewpoint of improving electromagnetic conversion characteristics.However, according to the studies of the inventors, it is found that, ina case where the center line average surface roughness Ra measuredregarding the surface of the magnetic layer is equal to or smaller than2.5 nm and any measures are not prepared, a decrease in resistance valueof the TMR head tends to occur even more significantly. However, even asignificant decrease in resistance value of the TMR head occurring in acase where the Ra is equal to or smaller than 2.5 nm can be prevented,in a case of the magnetic tape device according to one aspect of theinvention. In addition, the center line average surface roughness Rameasured regarding the surface of the magnetic layer can be equal to orgreater than 1.2 nm or equal to or greater than 1.3 nm. From a viewpointof improving electromagnetic conversion characteristics, a low value ofthe Ra is preferable, and thus, the Ra may be lower than the valuesdescribed above.

The surface smoothness of the magnetic layer, that is, the center lineaverage surface roughness Ra measured regarding the surface of themagnetic layer can be controlled by a well-known method. For example,the surface smoothness of the magnetic layer can be controlled byadjusting a size of various powder (for example, ferromagnetic powder,non-magnetic filler which may be arbitrarily included, and the like)included in the magnetic layer or manufacturing conditions of themagnetic tape.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on a non-magnetic support, or mayinclude a non-magnetic layer including non-magnetic powder and a bindingagent between the non-magnetic support and the magnetic layer. Thenon-magnetic powder used in the non-magnetic layer may be powder ofinorganic substances or powder of organic substances. In addition,carbon black and the like can be used. Examples of the inorganicsubstances include metal, metal oxide, metal carbonate, metal sulfate,metal nitride, metal carbide, and metal sulfide. These non-magneticpowder can be purchased as a commercially available product or can bemanufactured by a well-known method. For details thereof, descriptionsdisclosed in paragraphs 0146 to 0150 of JP2011-216149A can be referredto. For carbon black which can be used in the non-magnetic layer,descriptions disclosed in paragraphs 0040 and 0041 of JP2010-24113A canbe referred to. The content (filling percentage) of the non-magneticpowder of the non-magnetic layer is preferably 50 to 90 mass % and morepreferably 60 to 90 mass %.

In regards to other details of a binding agent or additives of thenon-magnetic layer, the well-known technology regarding the non-magneticlayer can be applied. In addition, in regards to the type and thecontent of the binding agent, and the type and the content of theadditive, for example, the well-known technology regarding the magneticlayer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magneticsupport (hereinafter, also simply referred to as a “support”),well-known components such as polyethylene terephthalate, polyethylenenaphthalate, polyamide, polyamide imide, aromatic polyamide subjected tobiaxial stretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or heatingtreatment may be performed with respect to these supports in advance.

Back Coating Layer

The magnetic tape can also include a back coating layer includingnon-magnetic powder and a binding agent on a surface side of thenon-magnetic support opposite to the surface provided with the magneticlayer. The back coating layer preferably includes any one or both ofcarbon black and inorganic powder. In regards to the binding agentincluded in the back coating layer and various additives which can bearbitrarily included in the back coating layer, a well-known technologyregarding the treatment of the magnetic layer and/or the non-magneticlayer can be applied.

Various Thickness

A thickness of the non-magnetic support is preferably 3.0 to 6.0 μm.

A thickness of the magnetic layer is preferably equal to or smaller than0.15 μm and more preferably equal to or smaller than 0.1 μm, from aviewpoint of realization of high-density recording required in recentyears. The thickness of the magnetic layer is even more preferably 0.01to 0.1 μm. The magnetic layer may be at least single layer, the magneticlayer may be separated into two or more layers having different magneticproperties, and a configuration of a well-known multilayered magneticlayer can be applied. A thickness of the magnetic layer in a case wherethe magnetic layer is separated into two or more layers is a totalthickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 μm.

Meanwhile, the magnetic tape is normally used to be accommodated andcirculated in a magnetic tape cartridge. In order to increase recordingcapacity for 1 reel of the magnetic tape cartridge, it is desired toincrease a total length of the magnetic tape accommodated in 1 reel ofthe magnetic tape cartridge. In order to increase the recordingcapacity, it is necessary that the magnetic tape is thinned(hereinafter, referred to as “thinning”). As one method of thinning themagnetic tape, a method of decreasing a total thickness of a magneticlayer and a non-magnetic layer of a magnetic tape including thenon-magnetic layer and the magnetic layer on a non-magnetic support inthis order is used. In a case where the magnetic tape includes anon-magnetic layer, the total thickness of the magnetic layer and thenon-magnetic layer is preferably equal to or smaller than 1.8 μm, morepreferably equal to or smaller than 1.5 μm, and even more preferablyequal to or smaller than 1.1 μm, from a viewpoint of thinning themagnetic tape. According to the studies of the inventors, it is foundthat, in a case where the total thickness of the magnetic layer and thenon-magnetic layer is equal to or smaller than 1.1 μm and any measuresare not prepared, a decrease in resistance value of the TMR head tendsto occur even more significantly. However, even a significant decreasein resistance value of the TMR head occurring in a case where the totalthickness of the magnetic layer and the non-magnetic layer is equal toor smaller than 1.1 μm can be prevented, in a case of the magnetic tapedevice according to one aspect of the invention. In addition, the totalthickness of the magnetic layer and the non-magnetic layer can be, forexample, equal to or greater than 0.1 μm or equal to or greater than 0.2μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.9 μm and even more preferably 0.1 to 0.7 μm.

The thicknesses of various layers of the magnetic tape and thenon-magnetic support can be acquired by a well-known film thicknessmeasurement method. As an example, a cross section of the magnetic tapein a thickness direction is, for example, exposed by a well-known methodof ion beams or microtome, and the exposed cross section is observedwith a scan electron microscope. In the cross section observation,various thicknesses can be acquired as a thickness acquired at oneposition of the cross section in the thickness direction, or anarithmetical mean of thicknesses acquired at a plurality of positions oftwo or more positions, for example, two positions which are arbitrarilyextracted. In addition, the thickness of each layer may be acquired as adesigned thickness calculated according to the manufacturing conditions.

Manufacturing Method

Preparation of Each Layer Forming Composition

Each composition for forming the magnetic layer, the non-magnetic layer,or the back coating layer normally includes a solvent, together withvarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magneticrecording medium can be used. Among those, from a viewpoint ofsolubility of the binding agent normally used in the coating typemagnetic recording medium, each layer forming composition preferablyincludes one or more ketone solvents such as acetone, methyl ethylketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone,isophorone, and tetrahydrofuran. The amount of the solvent of each layerforming composition is not particularly limited, and can be set to bethe same as that of each layer forming composition of a typical coatingtype magnetic recording medium. In addition, steps of preparing eachlayer forming composition generally include at least a kneading step, adispersing step, and a mixing step provided before and after thesesteps, if necessary. Each step may be divided into two or more stages.All of raw materials used in the invention may be added at an initialstage or in a middle stage of each step. In addition, each raw materialmay be separately added in two or more steps. For example, a bindingagent may be separately added in a kneading step, a dispersing step, anda mixing step for adjusting viscosity after the dispersion. In amanufacturing step of the magnetic tape, a well-known manufacturingtechnology of the related art can be used in a part of the step or inthe entire step. In the kneading step, an open kneader, a continuouskneader, a pressure kneader, or a kneader having a strong kneading forcesuch as an extruder is preferably used. The details of the kneadingprocesses of these kneaders are disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-79274A (JP-H01-79274A). In addition, inorder to disperse each layer forming composition, glass beads and/orother beads can be used. As such dispersion beads, zirconia beads,titania beads, and steel beads which are dispersion beads having highspecific gravity are preferable. These dispersion beads are preferablyused by optimizing a bead diameter and a filling percentage. As adispersing machine, a well-known dispersing machine can be used.

Coating Step

The magnetic layer can be formed, for example, by directly applying themagnetic layer forming composition onto the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. The back coating layer can be formed by applying the back coatinglayer forming composition to a side of the non-magnetic support oppositeto a side provided with the magnetic layer (or to be provided with themagnetic layer). For details of the coating for forming each layer, adescription disclosed in a paragraph 0066 of JP2010-231843A can bereferred to.

Other Steps

For details of various other steps for manufacturing the magnetic tape,descriptions disclosed in paragraphs 0067 to 0070 of JP2010-231843A canbe referred to. In addition, a servo pattern can also be formed in themagnetic tape by a well-known method, in order to perform head trackingservo in the magnetic tape device.

One Aspect of Preferred Manufacturing Method

As a preferred manufacturing method of the magnetic tape, amanufacturing method of applying vibration to the magnetic layer can beused, in order to improve uniformity of the thickness of the liquid filmof fatty acid ester on the surface of the magnetic layer. The inventorshave surmised that, by adding vibration, the liquid film of fatty acidester on the surface of the magnetic layer flows and the uniformity ofthe thickness of the liquid film is improved.

That is, the magnetic tape can be manufactured by a manufacturing methodof forming the magnetic layer by applying the magnetic layer formingcomposition including ferromagnetic powder, a binding agent, and fattyacid ester on the non-magnetic support and drying to form a magneticlayer, and applying vibration to the formed magnetic layer. Themanufacturing method is identical to the typical manufacturing method ofthe magnetic tape, except for applying vibration to the magnetic layer,and the details thereof are as described above.

Means for applying vibration are not particularly limited. For example,the vibration can be applied to the magnetic layer, by bringing thesurface of the non-magnetic support, provided with the magnetic layerformed, on a side opposite to the magnetic layer to come into contactwith a vibration imparting unit. The non-magnetic support, provided withthe magnetic layer formed, may run while coming into contact with avibration imparting unit. The vibration imparting unit, for example,includes an ultrasonic vibrator therein, and accordingly, vibration canbe applied to a product coming into contact with the unit. It ispossible to adjust the vibration applied to the magnetic layer by avibration frequency, and strength of the ultrasonic vibrator, and/or thecontact time with the vibration imparting unit. For example, the contacttime can be adjusted by a running speed of the non-magnetic support,provided with the magnetic layer formed, while coming into contact withthe vibration imparting unit. The vibration imparting conditions are notparticularly limited, and may be set so as to control the spacingdistribution, particularly, the full width at half maximum of thespacing distribution FWHM_(before) before vacuum heating. In order toset the vibration imparting conditions, a preliminary experiment can beperformed before the actual manufacturing, and the conditions can beoptimized.

In addition, the full width at half maximum of the spacing distributionFWHM_(after) after the vacuum heating tends to be decreased, in a casewhere the dispersion conditions of the magnetic layer formingcomposition are reinforced (for example, the number of times of thedispersion is increased, the dispersion time is extended, and the like),and/or the filtering conditions are reinforced (for example, a filterhaving a small hole diameter is used as a filter used in the filtering,the number of times of the filtering is increased, and the like). Theinventors have surmised that this is because the uniformity of theheight of the projection present on the surface of the magnetic layer isimproved, by improving dispersibility and/or the uniformity of theparticle size of the particulate matter included in the magnetic layerforming composition, particularly, the non-magnetic filler which mayfunction as the projection formation agent described above. Apreliminary experiment can be performed before the actual manufacturing,and the dispersion conditions and/or the filtering conditions can beoptimized.

In addition, in the magnetic tape including the magnetic layer includingcarbon black as the non-magnetic filler, it is effective to use thedispersing agent for improving dispersibility of the carbon black as amagnetic layer component, in order to decrease the full width at halfmaximum of the spacing distribution FWHM_(after) after the vacuumheating. For example, organic tertiary amine can be used as a dispersingagent of carbon black. For details of the organic tertiary amine,descriptions disclosed in paragraphs 0011 to 0018 and 0021 ofJP2013-049832A can be referred to. The organic tertiary amine is morepreferably trialkylamine. An alkyl group included in trialkylamine ispreferably an alkyl group having 1 to 18 carbon atoms. Three alkylgroups included in trialkylamine may be the same as each other ordifferent from each other. For details of the alkyl group, descriptionsdisclosed in paragraphs 0015 to 0016 of JP2013-049832A can be referredto. As trialkylamine, trioctylamine is particularly preferable.

Hereinabove, an aspect of the preferred manufacturing method of themagnetic tape has been described. However, the magnetic tape included inthe magnetic tape device according to one aspect of the invention is notlimited to a magnetic tape manufactured by the manufacturing methoddescribed above.

The magnetic tape described above is generally accommodated in amagnetic tape cartridge and the magnetic tape cartridge is mounted inthe magnetic tape device. In the magnetic tape cartridge, the magnetictape is generally accommodated in a cartridge main body in a state ofbeing wound around a reel. The reel is rotatably provided in thecartridge main body. As the magnetic tape cartridge, a single reel typemagnetic tape cartridge including one reel in a cartridge main body anda twin reel type magnetic tape cartridge including two reels in acartridge main body are widely used. In a case where the single reeltype magnetic tape cartridge is mounted in the magnetic tape device(drive) in order to record and/or reproduce data (magnetic signals) tothe magnetic tape, the magnetic tape is drawn from the magnetic tapecartridge and wound around the reel on the drive side. A magnetic headis disposed on a magnetic tape transportation path from the magnetictape cartridge to a winding reel. Sending and winding of the magnetictape are performed between a reel (supply reel) on the magnetic tapecartridge side and a reel (winding reel) on the drive side. In themeantime, the magnetic head comes into contact with and slides on thesurface of the magnetic layer of the magnetic tape, and accordingly, therecording and/or reproduction of the magnetic signal is performed. Withrespect to this, in the twin reel type magnetic tape cartridge, bothreels of the supply reel and the winding reel are provided in themagnetic tape cartridge. The magnetic tape according to one aspect ofthe invention may be accommodated in any of single reel type magnetictape cartridge and twin reel type magnetic tape cartridge. Theconfiguration of the magnetic tape cartridge is well known.

Reproducing Head

The magnetic tape device includes the TMR head as the reproducing head.The TMR head is a magnetic head including a tunnel magnetoresistanceeffect type element (TMR element). The TMR element can play a role ofdetecting a change in leakage magnetic field from the magnetic tape as achange in resistance value (electric resistance) by using a tunnelmagnetoresistance effect, as a reproducing element for reproducinginformation recorded on the magnetic tape (specifically, informationrecorded on the magnetic layer of the magnetic tape). By converting thedetected change in resistance value into a change in voltage, theinformation recorded on the magnetic tape can be reproduced.

As the TMR head included in the magnetic tape device, a TMR head havinga well-known configuration including a tunnel magnetoresistance effecttype element (TMR element) can be used. For example, for details of thestructure of the TMR head, materials of each unit configuring the TMRhead, and the like, well-known technologies regarding the TMR head canbe used.

The TMR head is a so-called thin film head. The TMR element included inthe TMR head at least includes two electrode layers, a tunnel barrierlayer, a free layer, and a fixed layer.

The TMR head includes a TMR element in a state where cross sections ofthese layers face a side of a surface sliding on the magnetic tape. Thetunnel barrier layer is positioned between the two electrode layers andthe tunnel barrier layer is an insulating layer. Meanwhile, the freelayer and the fixed layer are magnetic layers. The free layer is alsoreferred to as a magnetization free layer and is a layer in which amagnetization direction changes depending on the external magneticfield. On the other hand, the fixed layer is a layer in which amagnetization direction does not change depending on the externalmagnetic field. The tunnel barrier layer (insulating layer) ispositioned between the two electrodes, normally, and thus, even in acase where a voltage is applied, in general, a current does not flow ordoes not substantially flow. However, a current (tunnel current) flowsby the tunnel effect depending on a magnetization direction of the freelayer affected by a leakage magnetic field from the magnetic tape. Theamount of a tunnel current flow changes depending on a relative angle ofa magnetization direction of the fixed layer and a magnetizationdirection of the free layer, and as the relative angle decreases, theamount of the tunnel current flow increases. A change in amount of thetunnel current flow is detected as a change in resistance value by thetunnel magnetoresistance effect. By converting the change in resistancevalue into a change in voltage, the information recorded on the magnetictape can be reproduced. For an example of the configuration of the TMRhead, a description disclosed in FIG. 1 of JP2004-185676A can bereferred to, for example. However, there is no limitation to the aspectshown in the drawing. FIG. 1 of JP2004-185676A shows two electrodelayers and two shield layers. Here, a TMR head having a configuration inwhich the shield layer serves as an electrode layer is also well knownand the TMR head having such a configuration can also be used. In theTMR head, a current (tunnel current) flows between the two electrodesand thereby changing electric resistance, by the tunnelmagnetoresistance effect. The TMR head is a magnetic head having a CPPstructure, and thus, a direction in which a current flows is atransportation direction of the magnetic tape. In the invention and thespecification, the description regarding “orthogonal” includes a rangeof errors allowed in the technical field of the invention. For example,the range of errors means a range of less than ±10° from an exactorthogonal state, and the error from the exact orthogonal state ispreferably within ±5° and more preferably within ±30. A decrease inresistance value of the TMR head means a decrease in electric resistancemeasured by bringing an electric resistance measuring device intocontact with a wiring connecting two electrodes, and a decrease inelectric resistance between two electrodes in a state where a currentdoes not flow. A significant decrease in electric resistance causes adecrease in electromagnetic conversion characteristics. This decrease inresistance value of the TMR head can be prevented by using a magnetictape having the FWHM_(before), the FWHM_(after), and the difference(S_(after)−S_(before)) respectively in the ranges described above, asthe magnetic tape in which information to be reproduced is recorded.

The reproducing head is a magnetic head including at least the TMRelement as a reproducing element for reproducing information recorded onthe magnetic tape. Such a magnetic head may include or may not includean element for recording information in the magnetic tape. That is, thereproducing head and the recording head may be one magnetic head orseparated magnetic heads. In addition, the magnetic head including theTMR element as a reproducing element may include a servo pattern readingelement for performing head tracking servo.

As the magnetic tape transportation speed of the magnetic tape device ishigh, it is possible to shorten a reproducing time. Meanwhile, it isdesired that the magnetic tape transportation speed is decreased, inorder to prevent a deterioration in recording and reproducingcharacteristics. From a viewpoint of preventing a deterioration inrecording and reproducing characteristics, the magnetic tapetransportation speed is preferably equal to or lower than 18 m/sec, morepreferably equal to or lower than 15 m/sec, and even more preferablyequal to or lower than 10 m/sec. The magnetic tape transportation speedcan be, for example, equal to or higher than 1 m/sec.

The magnetic tape transportation speed is also referred to as a runningspeed, and is a relative speed between the magnetic tape and thereproducing head in a case where the magnetic tape is transported (runs)in the magnetic tape device in order to reproduce information recordedon the magnetic tape. Normally, the magnetic tape transportation speedis set in a control unit of the magnetic tape device. As the magnetictape transportation speed is low, the time for which the same portion ofthe TMR head comes into contact with the magnetic tape increases at thetime of reproducing, and accordingly, damage on the TMR head more easilyoccurs and a decrease in resistance value easily occurs. In the magnetictape device according to one aspect of the invention, such a decrease inresistance value can be prevented by using a magnetic tape having theFWHM_(before), the FWHM_(after), and the difference(S_(after)−S_(before)) respectively in the ranges described above.

Magnetic Reproducing Method

One aspect of the invention relates to a magnetic reproducing methodincluding: reproducing information recorded on a magnetic tape by areproducing head, in which the reproducing head is a magnetic headincluding a tunnel magnetoresistance effect type element as areproducing element, the magnetic tape includes a non-magnetic support,and a magnetic layer including ferromagnetic powder, a binding agent,and fatty acid ester on the non-magnetic support, a full width at halfmaximum of spacing distribution measured by optical interferometryregarding the surface of the magnetic layer before performing a vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 7.0 nm, a full width at half maximum of spacingdistribution measured by optical interferometry regarding the surface ofthe magnetic layer after performing the vacuum heating with respect tothe magnetic tape is greater than 0 nm and equal to or smaller than 7.0nm, and a difference (S_(after)−S_(before)) between a spacing S_(after)measured by optical interferometry regarding the surface of the magneticlayer after performing the vacuum heating with respect to the magnetictape and a spacing S_(before) measured by optical interferometryregarding the surface of the magnetic layer before performing the vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 9.0 nm. The reproducing of the information recordedon the magnetic tape is performed by bringing the magnetic tape intocontact with the reproducing head allowing sliding while transporting(causing running of) the magnetic tape. The details of the reproducingof the magnetic reproducing method and the details of the magnetic tapeand the reproducing head used in the magnetic reproducing method are asthe descriptions regarding the magnetic tape device according to oneaspect of the invention.

According to one aspect of the invention, a magnetic tape used in amagnetic tape device in which a TMR head is used as a reproducing head,the magnetic tape including: a magnetic layer including ferromagneticpowder, a binding agent, and fatty acid ester on a non-magnetic support,a full width at half maximum of spacing distribution measured by opticalinterferometry regarding the surface of the magnetic layer beforeperforming a vacuum heating with respect to the magnetic tape is greaterthan 0 nm and equal to or smaller than 7.0 nm, a full width at halfmaximum of spacing distribution measured by optical interferometryregarding the surface of the magnetic layer after performing the vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 7.0 nm, and a difference (S_(after)−S_(before))between a spacing S_(after) measured by optical interferometry regardingthe surface of the magnetic layer after performing the vacuum heatingwith respect to the magnetic tape and a spacing S_(before) measured byoptical interferometry regarding the surface of the magnetic layerbefore performing the vacuum heating with respect to the magnetic tapeis greater than 0 nm and equal to or smaller than 9.0 nm, is alsoprovided. The details of the magnetic tape are also as the descriptionsregarding the magnetic tape device according to one aspect of theinvention.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to aspects shown in the examples.“Parts” and “%” in the following description mean “parts by mass” and“mass %”, unless otherwise noted.

1. Manufacturing of Magnetic Tape Example 1

Magnetic Layer Forming Composition

Magnetic Solution

Ferromagnetic hexagonal barium ferrite powder: 100.0 parts

-   -   (coercivity Hc: 2,100 Oe (168 kA/m), average particle size: 25        nm)

Sulfonic acid-containing polyurethane resin: 15.0 parts

Cyclohexanone: 150.0 parts

Methyl ethyl ketone: 150.0 parts

Abrasive Liquid

α-alumina (average particle size of 110 nm): 9.0 parts

A vinyl chloride copolymer: (MR110 manufactured by Zeon Corporation):0.7 parts

Cyclohexanone: 20.0 parts

Silica Sol

Colloidal silica prepared by a sol-gel method (average particle size:120 nm): 3.5 parts

Methyl ethyl ketone: 8.2 parts

Other Components

Butyl stearate: 1.0 part

Stearic acid: 1.0 part

Polyisocyanate (CORONATE manufactured by Nippon Polyurethane IndustryCo., Ltd.): 2.5 parts

Finishing Additive Solvent

Cyclohexanone: 180.0 parts

Methyl ethyl ketone: 180.0 parts

Non-Magnetic Layer Forming Composition

Non-magnetic inorganic powder (α-iron oxide): 80.0 parts

(average particle size: 0.15 μm, average acicular ratio: 7,Brunauer-Emmett-Teller (BET) specific surface area: 52 m²/g)

Carbon black (average particle size of 20 nm): 20.0 parts

An electron beam-curable vinyl chloride copolymer: 13.0 parts

An electron beam-curable polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Butyl stearate: see Table 1

Stearic acid: see Table 1

Back Coating Layer Forming Composition

-   -   Non-magnetic inorganic powder (α-iron oxide): 80.0 parts

(average particle size: 0.15 μm, average acicular ratio: 7, BET specificsurface area: 52 m²/g)

Carbon black (average particle size of 20 nm): 20.0 parts

Carbon black (average particle size of 100 nm): 3.0 parts

A vinyl chloride copolymer: 13.0 parts

A sulfonic acid-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Stearic acid: 3.0 parts

Polyisocyanate (CORONATE manufactured by Nippon Polyurethane IndustryCo., Ltd.): 5.0 parts

Methyl ethyl ketone: 400.0 parts

Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

The magnetic solution was kneaded and diluted by an open kneader, andsubjected to a dispersion process of 12 passes, with a transverse beadsmill dispersing device and zirconia (ZrO₂) beads (hereinafter, referredto as “Zr beads”) having a bead diameter of 0.5 mm, by setting a beadfilling percentage as 80 volume %, a circumferential speed of rotordistal end as 10 m/sec, and a retention time for 1 pass as 2 minutes.

After mixing the components described above, the abrasive liquid was putin a vertical sand mill dispersing device together with Zr beads havinga bead diameter of 1 mm, the bead volume/(abrasive liquid volume+beadvolume) was adjusted to be 60%, the sand mill dispersing process wasperformed for 180 minutes, a solution after the process was extracted,and an ultrasonic dispersion filtering process was performed with aflow-type ultrasonic dispersion filtering device.

The magnetic solution, the silica sol, the abrasive liquid, othercomponents, and the finishing additive solvent were introduced into adissolver stirring device, and were stirred at a circumferential speedof 10 m/sec for 30 minutes. After that, the treatment was performed witha flow-type ultrasonic dispersing device at a flow rate of 7.5 kg/minfor the number of times of the passes shown in Table 1, and then, amagnetic layer forming composition was prepared by performing filteringwith a filter having a hole diameter shown in Table 1, for the number oftimes of the passes shown in Table 1.

The non-magnetic layer forming composition was prepared by the followingmethod.

Each component excluding a lubricant (butyl stearate and stearic acid)was kneaded with an open kneader and diluted, and then, was dispersed byusing a transverse bead mill dispersing device. After that, thelubricant (butyl stearate and stearic acid) was added thereto, andstirred and mixed with a dissolver stirring device, to prepare anon-magnetic layer forming composition.

The back coating layer forming composition was prepared by the followingmethod.

Each component excluding the lubricant (stearic acid), polyisocyanate,and methyl ethyl ketone (400.0 parts) was kneaded with an open kneaderand diluted, and then, was dispersed by using a transverse bead milldispersing device. After that, the lubricant (stearic acid),polyisocyanate, and methyl ethyl ketone (400.0 parts) were addedthereto, and stirred and mixed with a dissolver stirring device, toprepare a back coating layer forming composition.

Manufacturing of Magnetic Tape

The non-magnetic layer forming composition was applied onto apolyethylene naphthalate support having a thickness of 5.0 μm and driedso that the thickness after the drying becomes the thickness shown inTable 1, and then, an electron beam was emitted with an energy of 40 kGyat an acceleration voltage of 125 kV. The magnetic layer formingcomposition was applied thereto and dried so that the thickness afterthe drying becomes the thickness shown in Table 1, to form a coatinglayer of the magnetic layer forming composition.

After that, the support, provided with the coating layer formed, wasinstalled in a vibration imparting device shown in FIG. 1 so that thesurface thereof on a side opposite to the surface where the coatinglayer is formed comes into contact with the vibration imparting unit,and the support (in FIG. 1, reference numeral 101), provided with thecoating layer formed, was transported at a transportation speed of 0.5m/sec, to apply vibration to the coating layer. In FIG. 1, a referencenumeral 102 denotes a guide roller (a reference numeral 102 denotes oneof two guide rollers), a reference numeral 103 denotes the vibrationimparting device (vibration imparting unit including the ultrasonicvibrator), and an arrow denotes a transportation direction. The timefrom the start of the contact of the arbitrary portion of the support,provided with the coating layer formed, with the vibration impartingunit until the end of the contact (vibration imparting time) is shown inTable 1 as the imparting time. The vibration imparting unit usedincludes an ultrasonic vibrator therein. The vibration was imparted bysetting a vibration frequency and the intensity of the ultrasonicvibrator as values shown in Table 1.

After that, the back coating layer forming composition was applied ontothe surface of the support on a side opposite to the surface where thenon-magnetic layer and the magnetic layer are formed, and dried so thatthe thickness after the drying becomes thickness of 0.5 μm.

After that, the surface smoothing treatment (calender process) wasperformed with a calender roll configured of only a metal roll, at acalender process speed of 80 m/min, linear pressure of 300 kg/cm (294kN/m), and a surface temperature of a calender roll shown in Table 1. Asthe calender process conditions are reinforced (for example, as thesurface temperature of the calender roll increases), the center lineaverage surface roughness Ra measured regarding the surface of themagnetic layer tends to decrease.

Then, the thermal treatment was performed in the environment of theatmosphere temperature of 70° C. for 36 hours. After the thermaltreatment, slitting was performed so as to have a width of ½ inches(0.0127 meters), and the surface of the magnetic layer was cleaned witha tape cleaning device in which a nonwoven fabric and a razor blade areattached to a device including a sending and winding devices of the slitso as to press the surface of the magnetic layer. Then, a servo patternwas formed on the magnetic layer by a commercially available servowriter.

By doing so, a magnetic tape was obtained. The thickness of each layerof the manufactured magnetic tape was acquired by the following method.It was confirmed that the thicknesses of the formed non-magnetic layerand the magnetic layer were the thicknesses shown in Table 1 and thethicknesses of the back coating layer and the non-magnetic support werethe thicknesses described above.

A cross section of the magnetic tape in a thickness direction wasexposed to ion beams and the exposed cross section was observed with ascanning electron microscope. Various thicknesses were obtained as anarithmetical mean of thicknesses obtained at two portions in thethickness direction in the cross section observation.

A part of the magnetic tape manufactured by the method described abovewas used in the evaluation described below, and the other part was usedin order to measure a resistance value of the TMR head which will bedescribed later.

2. Evaluation of Physical Properties of Magnetic Tape

(1) Center Line Average Surface Roughness Ra Measured Regarding Surfaceof Magnetic Layer

The measurement regarding a measurement area of 40 μm×40 μm in thesurface of the magnetic layer of the magnetic tape was performed with anatomic force microscope (AFM, Nanoscope 4 manufactured by VeecoInstruments, Inc.), and a center line average surface roughness Ra wasacquired. A scan speed (probe movement speed) was set as 40 μm/sec and aresolution was set as 512 pixel×512 pixel.

(2) Full Width at Half Maximum of Spacing Distributions FWHM_(before)and FWHM_(after) Before and after Vacuum Heating

The full width at half maximum of the spacing distributionsFWHM_(before) and FWHM_(after) before and after vacuum heating wereacquired by the following method by using a tape spacing analyzer (TSA)(manufactured by Micro Physics, Inc.).

In a state where a glass sheet included in the TSA was disposed on thesurface of the magnetic layer of the magnetic tape, a hemisphere waspressed against the surface of the back coating layer of the magnetictape at a pressure of 5.05×10⁴ N/m (0.5 atm) by using a hemisphere madeof urethane included in the TSA as a pressing member. In this state, agiven region (150,000 to 200,000 μm²) of the surface of the magneticlayer of the magnetic tape was irradiated with white light from astroboscope included in the TSA through the glass sheet, and theobtained reflected light was received by a charge-coupled device (CCD)through an interference filter (filter selectively passing light at awavelength of 633 nm), and thus, an interference fringe image generatedon the uneven part of the region was obtained.

This image was divided into 300,000 points, a distance (spacing) betweenthe surface of the glass sheet on the magnetic tape side and the surfaceof the magnetic layer of the magnetic tape was acquired, and the fullwidth at half maximum of spacing distribution was full width at halfmaximum, in a case where this spacing was shown with a histogram, andthis histogram was fit with Gaussian distribution.

The vacuum heating was performed by storing the magnetic tape in avacuum constant temperature drying machine with a degree of vacuum of200 Pa to 0.01 Mpa and at inner atmosphere temperature of 70° C. to 90°C. for 24 hours.

(3) Difference (S_(after)−S_(before))

The difference (S_(after)−S_(before)) was a value obtained bysubtracting a mode of the histogram before the vacuum heating from amode of the histogram after the vacuum heating obtained in the section(2).

3. Measurement of Resistance Value of Reproducing Head

The magnetic tape manufactured in the part 1. was attached to a reeltester having a width of ½ inches (0.0127 meters) fixed to a recordinghead and a reproducing head, and information was recorded andreproduced. As the recording head, a metal-in-gap (MIG) head (gap lengthof 0.15 μm, track width of 1.0 μm) was used, and the reproducing head, aTMR head (element width of 70 nm) commercially available as areproducing head for HDD was used. A tape length of the magnetic tapewas 1,000 m, and a total of 4,000 passes of the transportation (running)of the magnetic tape was performed by setting the magnetic tapetransportation speed (relative speed of the magnetic tape and themagnetic head) at the time of performing reproducing as 4 m/sec. Thereproducing head was moved in a width direction of the magnetic tape by2.5 μm for 1 pass, a resistance value (electric resistance) of thereproducing head for transportation of 400 passes was measured, and arate of a decrease in resistance value with respect to an initial value(resistance value at 0 pass) was obtained by the following equation.Rate of decrease in resistance value (%)=[(initial value−resistancevalue after transportation of 400 passes)/initial value]×100

The measurement of the resistance value (electric resistance) wasperformed by bringing an electric resistance measuring device (digitalmulti-meter (product number: DA-50C) manufactured by Sanwa ElectricInstrument Co., Ltd.) into contact with a wiring connecting twoelectrodes of a TMR element included in a TMR head. In a case where thecalculated rate of a decrease in resistance value was equal to orgreater than 30%/o, it was determined that a decrease in resistancevalue occurred. Then, a reproducing head was replaced with a new head,and transportation after 400 passes was performed and a resistance valuewas measured. The number of times of occurrence of a decrease inresistance value which is 1 or greater indicates a significant decreasein resistance value. In the running of 4,000 passes, in a case where therate of a decrease in resistance value did not become equal to orgreater than 30%, the number of times of occurrence of a decrease inresistance value was set as 0. In a case where the number of times ofoccurrence of a decrease in resistance value is 0, the maximum value ofthe measured rate of a decrease in resistance value is shown in Table 1.

Examples 2 to 6 and Comparative Examples 1 to 17

1. Manufacturing of Magnetic Tape

A magnetic tape was manufactured in the same manner as in Example 1,except that various conditions shown in Table 1 were changed as shown inTable 1.

2. Evaluation of Physical Properties of Magnetic Tape

Various physical properties of the manufactured magnetic tape wereevaluated in the same manner as in Example 1.

3. Measurement of Resistance Value of Reproducing Head

A resistance value of the reproducing head was measured by the samemethod as that in Example 1, by using the manufactured magnetic tape. InExamples 2 to 6 and Comparative Examples 11 to 17, the TMR head whichwas the same as that in Example 1 was used as a reproducing head. InComparative Examples 1 to 10, a commercially available spin valve typeGMR head (element width of 70 nm) was used as a reproducing head. ThisGMR head was a magnetic head having a CIP structure including twoelectrodes with an MR element interposed therebetween in a directionorthogonal to the transportation direction of the magnetic tape. Aresistance value was measured in the same manner as in Example 1, bybringing an electric resistance measuring device into contact with awiring connecting these two electrodes.

The results of the evaluations described above are shown in Table 1.

TABLE 1 Unit Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Non-magnetic Butyl stearate Content Part 4.0 4.0 4.0 4.0 4.0 4.0 layerforming Stearic acid Content Part 1.0 1.0 1.0 1.0 1.0 1.0 compositionManufacturing Calender Temperature of ° C. 75 80 95 95 95 95 conditionsprocess conditions calender roll Ultrasonic vibration Imparting time Sec0.5 0.5 0.5 0.5 3.0 3.0 imparting conditions Frequency kHz 30 30 30 3030 30 Intensity W 100 100 100 100 100 100 Magnetic layer Number of Times1 2 2 2 30 30 forming times of composition passes of flow- preparationtype ultrasonic conditions dispersing device Number of times Times 1 1 11 5 5 of filtering Filter hole diameter μm 1.0 1.0 1.0 1.0 0.5 0.5Physical Center line average surface nm 2.8 2.5 2.0 2.0 2.0 2.0properties roughness Ra measured regarding surface of magnetic layerMagnetic layer Thickness μm 0.1 0.1 0.1 0.1 0.1 0.1 Non-magneticThickness μm 1.5 1.0 0.5 0.3 0.5 0.3 layer Non-magnetic Total thicknessμm 1.6 1.1 0.6 0.4 0.6 0.4 layer + Magnetic layer S_(after) − S_(before)nm 8.9 6.0 3.2 3.1 3.2 3.2 FWHM_(before) nm 6.8 6.7 6.8 6.8 4.1 4.1FWHM_(after) nm 6.9 6.8 6.9 6.9 4.0 4.0 Reproducing Kind — TMR TMR TMRTMR TMR TMR head Performance Number of times of occurrence of Times 0 00 0 0 0 decrease in resistance value (times) Rate of decrease inresistance value (%) % 7 8 9 11 3 5 Comparative Comparative ComparativeComparative Comparative Unit Example 1 Example 2 Example 3 Example 4Example 5 Non-magnetic layer Butyl stearate Content Part 4.0 4.0 4.0 4.04.0 forming Stearic acid Content Part 1.0 1.0 1.0 1.0 1.0 compositionManufacturing Calender process Temperature of ° C. 75 80 95 80 95conditions conditions calender roll Ultrasonic Imparting time Sec NoneNone None None None vibration Frequency KHz imparting Intensity Wconditions Magnetic layer Number of times Times 2 2 2 2 2 forming ofpasses of composition flow-type preparation ultrasonic conditionsdispersing device Number of times Times 1 1 1 1 1 of filtering Filterhole μm 1.0 1.0 1.0 1.0 1.0 diameter Physical properties Center lineaverage surface nm 2.8 2.5 2.0 2.5 2.0 roughness Ra measured regardingsurface of magnetic layer Magnetic layer Thickness μm 0.1 0.1 0.1 0.10.1 Non-magnetic Thickness μm 1.5 1.0 1.0 0.5 0.5 layer Non-magneticTotal thickness μm 1.6 1.1 1.1 0.6 0.6 layer + Magnetic layer S_(after)− S_(before) nm 8.9 6.0 5.9 3.2 3.1 FWHM_(before) nm 8.7 8.8 8.5 8.6 8.6FWHM_(after) nm 6.8 6.8 6.8 6.9 6.8 Reproducing head Kind — GMR GMR GMRGMR GMR Performance Number of times of occurrence of Times 0 0 0 0 0decrease in resistance value (times) Rate of decrease in resistance % 00 0 0 0 value (%) Comparative Comparative Comparative ComparativeComparative Unit Example 6 Example 7 Example 8 Example 9 Example 10Non-magnetic layer Butyl stearate Content Part 8.0 4.0 15.0 0.0 4.0forming Stearic acid Content Part 1.0 1.0 1.0 1.0 2.0 compositionManufacturing Calender process Temperature of ° C. 95 95 95 95 95conditions conditions calender roll Ultrasonic Imparting time Sec None0.5 0.5 0.5 None vibration Frequency KHz 30 30 30 imparting Intensity W100 100 100 conditions Magnetic layer Number of times Times 2 1 2 2 2forming of passes of composition flow-type preparation ultrasonicconditions dispersing device Number of times Times 1 1 1 1 1 offiltering Filter hole μm 1.0 1.0 1.0 1.0 1.0 diameter Physicalproperties Center line average surface nm 2.0 2.0 2.0 2.0 2.0 roughnessRa measured regarding surface of magnetic layer Magnetic layer Thicknessμm 0.1 0.1 0.1 0.1 0.1 Non-magnetic Thickness μm 0.5 0.5 0.5 0.5 0.5layer Non-magnetic Total thickness μm 0.6 0.6 0.6 0.6 0.6 layer +Magnetic layer S_(after) − S_(before) nm 6.1 3.1 11.0 0 3.2FWHM_(before) nm 8.5 6.8 6.9 6.8 8.5 FWHM_(after) nm 6.8 7.5 6.9 7.0 7.0Reproducing head Kind — GMR GMR GMR GMR GMR Performance Number of timesof occurrence of Times 0 0 0 0 0 decrease in resistance value (times)Rate of decrease in resistance % 0 0 0 0 0 value (%) ComparativeComparative Comparative Comparative Unit Example 11 Example 12 Example13 Example 14 Non-magnetic layer Butyl stearate Content Part 4.0 4.0 4.04.0 forming composition Stearic acid Content Part 1.0 1.0 1.0 1.0Manufacturing conditions Calender process conditions Temperature of ° C.75 80 95 95 calender roll Ultrasonic vibration imparting Imparting timeSec None None None 0.5 conditions Frequency kHz 30 Intensity W 100Magnetic layer forming Number of times Times 2 2 2 1 compositionpreparation of passes of conditions flew-type ultrasonic dispersingdevice Number of times Times 1 1 1 1 of filtering Filter hole μm 1.0 1.01.0 1.0 diameter Physical properties Center line average surfaceroughness Ra nm 2.8 2.5 2.0 2.0 measured regarding surface of magneticlayer Magnetic layer Thickness μm 0.1 0.1 0.1 0.1 Non-magnetic layerThickness μm 1.5 1.0 0.5 0.5 Non-magnetic layer + Total thickness μm 1.61.1 0.6 0.6 Magnetic layer S_(after) − S_(before) nm 8.9 6.0 3.2 3.1FWHM_(before) nm 8.7 8.8 8.5 6.8 FWHM_(after) nm 6.9 6.8 6.9 7.5Reproducing head Kind — TMR TMR TMR TMR Performance Number of times ofoccurrence of decrease in Times 1 3 8 7 resistance value (times) Rate ofdecrease in resistance value (%) % — — — — Comparative ComparativeComparative Unit Example15 Example 16 Example 17 Non-magnetic layerButyl stearate Content Part 15.0 0.0 4.0 forming composition Stearicacid Content Part 1.0 1.0 1.0 Manufacturing conditions Calender processconditions Temperature of ° C. 95 95 95 calender roll Ultrasonicvibration imparting Imparting time Sec 0.5 0.5 None conditions FrequencykHz 30 30 Intensity W 100 100 Magnetic layer forming Number of timesTimes 2 2 2 composition preparation of passes of conditions flew-typeultrasonic dispersing device Number of times Times 1 1 1 of filteringFilter hole μm 1.0 1.0 1.0 diameter Physical properties Center lineaverage surface roughness Ra nm 2.0 2.0 2.0 measured regarding surfaceof magnetic layer Magnetic layer Thickness μm 0.1 0.1 0.1 Non-magneticlayer Thickness μm 0.5 0.5 0.3 Non-magnetic layer + Total thickness μm0.6 0.6 0.4 Magnetic layer S_(after) − S_(before) nm 11.0 0 3.1FWHM_(before) nm 6.9 6.8 8.6 FWHM_(after) nm 6.9 7.0 6.9 Reproducinghead Kind — TMR TMR TMR Performance Number of times of occurrence ofdecrease in Times 10 10 9 resistance value (times) Rate of decrease inresistance value (%) % — — —

As shown in Table 1, in Comparative Examples 1 to 10 in which the GMRhead was used as a reproducing head, even in a case where any one of theFWHM_(before) and the FWHM_(after) of the magnetic tape and thedifference (S_(after)−S_(before)) was not in the range described above,a significant decrease in resistance value of the reproducing head wasnot observed. On the other hand, in Comparative Examples 11 to 17 inwhich the TMR head was used as a reproducing head, and any one of theFWHM_(before) and the FWHM_(after) of the magnetic tape, and thedifference (S_(after)−S_(before)) was not in the range described above,a significant decrease in resistance value of the reproducing headoccurred.

With respect to this, in Examples 1 to 6 in which the TMR head was usedas a reproducing head, and the FWHM_(before), the FWHM_(after), and thedifference (S_(after)−S_(before)) were respectively in the rangesdescribed above, it was possible to prevent a significant decrease inresistance value of the reproducing head.

One aspect of the invention is effective for usage of magnetic recordingfor which high-sensitivity reproducing of information recorded with highdensity is desired.

What is claimed is:
 1. A magnetic tape device comprising: a magnetictape; and a reproducing head, wherein the reproducing head is a magnetichead including a tunnel magnetoresistance effect type element as areproducing element, the magnetic tape includes a non-magnetic support,and a magnetic layer including ferromagnetic powder, a binding agent,and fatty acid ester on the non-magnetic support, a full width at halfmaximum of spacing distribution measured by optical interferometryregarding a surface of the magnetic layer before performing a vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 7.0 nm, a full width at half maximum of spacingdistribution measured by optical interferometry regarding the surface ofthe magnetic layer after performing the vacuum heating with respect tothe magnetic tape is greater than 0 nm and equal to or smaller than 7.0nm, and a difference (S_(after)−S_(before)) between a spacing S_(after)measured by optical interferometry regarding the surface of the magneticlayer after performing the vacuum heating with respect to the magnetictape and a spacing S_(before) measured by optical interferometryregarding the surface of the magnetic layer before performing the vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 9.0 nm.
 2. The magnetic tape device according toclaim 1, wherein the full width at half maximum of spacing distributionmeasured by optical interferometry regarding the surface of the magneticlayer before performing the vacuum heating with respect to the magnetictape is 3.0 nm to 7.0 nm.
 3. The magnetic tape device according to claim1, wherein the full width at half maximum of spacing distributionmeasured by optical interferometry regarding the surface of the magneticlayer after performing the vacuum heating with respect to the magnetictape is 3.0 nm to 7.0 nm.
 4. The magnetic tape device according to claim1, wherein the difference (S_(after)−S_(before)) is 2.0 nm to 9.0 nm. 5.The magnetic tape device according to claim 1, wherein a center lineaverage surface roughness Ra measured regarding a surface of themagnetic layer is equal to or smaller than 2.8 nm.
 6. The magnetic tapedevice according to claim 5, wherein the center line average surfaceroughness Ra is equal to or smaller than 2.5 nm.
 7. The magnetic tapedevice according to claim 1, wherein the magnetic tape includes anon-magnetic layer including non-magnetic powder and a binding agentbetween the non-magnetic support and the magnetic layer, and a totalthickness of the magnetic layer and the non-magnetic layer is equal toor smaller than 1.8 μm.
 8. The magnetic tape device according to claim7, wherein the total thickness of the magnetic layer and thenon-magnetic layer is equal to or smaller than 1.1 μm.
 9. A magneticreproducing method comprising: reproducing information, recorded on amagnetic tape, by a reproducing head, wherein the reproducing head is amagnetic head including a tunnel magnetoresistance effect type elementas a reproducing element, the magnetic tape includes a non-magneticsupport, and a magnetic layer including ferromagnetic powder, a bindingagent, and fatty acid ester on the non-magnetic support, a full width athalf maximum of spacing distribution measured by optical interferometryregarding a surface of the magnetic layer before performing a vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 7.0 nm, a full width at half maximum of spacingdistribution measured by optical interferometry regarding the surface ofthe magnetic layer after performing the vacuum heating with respect tothe magnetic tape is greater than 0 nm and equal to or smaller than 7.0nm, and a difference (S_(after)-S_(before)) between a spacing S_(after)measured by optical interferometry regarding the surface of the magneticlayer after performing the vacuum heating with respect to the magnetictape and a spacing S_(before) measured by optical interferometryregarding the surface of the magnetic layer before performing the vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 9.0 nm.
 10. The magnetic reproducing method accordingto claim 9, wherein the full width at half maximum of spacingdistribution measured by optical interferometry regarding the surface ofthe magnetic layer before performing a vacuum heating with respect tothe magnetic tape is 3.0 nm to 7.0 nm.
 11. The magnetic reproducingmethod according to claim 9, wherein the full width at half maximum ofspacing distribution measured by optical interferometry regarding thesurface of the magnetic layer after performing the vacuum heating withrespect to the magnetic tape is 3.0 nm to 7.0 nm.
 12. The magneticreproducing method according to claim 9, wherein the difference(S_(after)-S_(before)) is 2.0 nm to 9.0 nm.
 13. The magnetic reproducingmethod according to claim 9, wherein a center line average surfaceroughness Ra measured regarding a surface of the magnetic layer is equalto or smaller than 2.8 nm.
 14. The magnetic reproducing method accordingto claim 13, wherein the center line average surface roughness Ra isequal to or smaller than 2.5 nm.
 15. The magnetic reproducing methodaccording to claim 9, wherein the magnetic tape includes a non-magneticlayer including non-magnetic powder and a binding agent between thenon-magnetic support and the magnetic layer, and a total thickness ofthe magnetic layer and the non-magnetic layer is equal to or smallerthan 1.8 μm.
 16. The magnetic reproducing method according to claim 15,wherein the total thickness of the magnetic layer and the non-magneticlayer is equal to or smaller than 1.1 μm.